Arc torch and process



Sept. 10, 1957 R. M. GAGE ARC TORCH AND PROCESS 3 Sheets-Sheet 1 Filed July 26, 1955 DISTANCE FROM CATHODE CURRENT-AMPS. INVENTOR RQBERT M. GAGE BY WWO? I'd/M ATTORNEY Sept. 10, 1957 R. M. GAGE ARC TORCH AND PROCESS s Sheet-Sheet 2 Filed July 26. 1955 --n////// W M w -5 Z m y Vw a F- G M R mu m N m n ET 0 R T N T B A o R Sept. 10, 1957 R. M. GAGE ARC TORCH AND PROCESS Sheets-Sheet 3 Filed July 26, 1955 l I 200 AMP. CFH. ARGON ARC TORCH OPEN ARC\ I so ZQ/Z.

AXIAL ELECTRlC FIELD IN NOZZLE -VOLTS/ IN.

K R O w C R A DELIVERED 290 AMP. 2 NOZZLE %'ARc OPEN ARC mPTJ?) 1o ARGON NOZZLE FLOW'CFH.

kx mukom ATTORIfIY g 7- X '7. X 50 7- ARGON O ARGON E m m6 I l E B i m 6 m M m w n| ml N N N E G o M R VD: H w m l E mm O iOO'IQZTFfGON NOZZLE GAS MIXTURE-7. BY VOLUME United States Patent Ofifice 2,806,124 Patented Sept. 10, 1957 ARC TORCH AND PROCESS Robert M. Gage, Bnifalo, N. Y., assignor to Union Carbide Corporation, a corporation of New York Application July 26, 1955, Serial No. 524,353

29 Claims. (Cl. 219-121) This invention relates to high-pressure electric arcs and more particularly to a fundamentally novel are process and apparatus.

Briefly, according to the invention there is provided a process which comprises establishing a high-pressure are between an electrode and a workpiece, wall-stabilizing a portion of the length of the arc, to produce and control the shape and direction of an effluent between the point of the wall-stabilization and the workpiece, and applying the so-controlled cflluent to the workpiece.

Further, according to the invention, there is provided an arc torch comprising an arc electrode, and means having a passage through which the arc and the arc gases pass. Such torch is provided with a non-consumable solid wall which laterally restricts the arc and gases and which passages discharges a current-carrying effluent. Such effluent a stable, directional and shaped so as to follow a well-defined path the cross-section of which is determined by the geometry of the passage.

The principal feature of the invention is the use of suitable means such as a non-consumable nozzle composed of a cooled solid material having arc passage means from which an electric current carrying efiiuent issues. Such passage wall-stabilizes, laterally shapes and/or constricts the arc, concentrating or redistributing the energy thereof, defines the shape and direction of the etlluent, and discharges the latter.

The novel combination and extension of such physical principles of wall-stabilization and construction is effectively applied, according to the present invention, to cutting and welding arcs, as well as to other material heating arcs, at currents of the order of hundreds and even thousands of amperes, with strikingly unexpected and useful results, as will be explained below.

The invention can be explained by considering first a conventional non-consumable electrode-inert gas shielded arc-type set-up with a tungsten electrode above, a metal workpiece-electrode below, and a gas supplied around the electrode and are to shield the electrode from the air. With such set-up is combined, according to the invention, a water-cooled collar or nozzle of metal, for example, which surrounds and laterally confines a portion of the arc-column at or just below the tungsten electrode in a manner which wall-stabilizes and constricts, to some degree, the surrounded portion of the are. It should be emphasized that to be effective such nozzle should have a maximum orifice diameter at least small enough so that the arc portion within it does not appreciably deviate in direction on account of otherwise disturbing influences such as random magnetic fields, gaseous convection and erratic behavior at the electrodes.

The criterion used herein is that if a given are portion is observedly wall-stabilized, the nozzle orifice is sufficiently proximate to the arc to accomplish the purposes of the invention. The orifice can be made much Smaller with additional remarkable results as will be shown below. The minimum length of the so-surrounded portion of the arc does not seem to be critical, at least down to that compatible with mechanical requirements of cooling the nozzle against the intense heating effect.

The are portion between the outlet of the arc-stabilizing nozzle and the workpiece has its initial direction fixed by wall-stabilization and has stiffness and persistence of direction. This directional fixing of such are portion is a great improvement over the prior art. The stiffness of the arc is, however, additionally dependent upon the flow of gas entering the torch electrode end of the nozzle. It is convenient and preferred that a controllable supply of gas be introduced to the nozzle orifice and be regulated to control the stiffness and momentum of the effluent, and also to more effectively extend the advantages of wallstabilization thereto. This flow of gas also materially aids in transferring to the work heat which otherwise would go to the nozzle. This reduces the problem of cooling the nozzle.

It has been mentioned that although there is a maximum size nozzle orifice for wall-stabilizing a given portion of the arc, the orifice can be made much smaller with highly beneficial and useful results. It has been discovered that a cooled metal nozzle of the invention can be used, not only to wall-stabilize metal working or material heating arcs but, by using smaller orifices, can also constrict the are thereby increasing the arc voltage and total are power at a given current. Under such conditions the flow of gas through the nozzle causes an additional increase in arc voltage and power because much of the flowing gas becomes part of the arc and must be heated to arc temperatures (8000 K. to 20,000 K., estimated for argon).

Also, because the arc stream and gas jet, as they issue from the nozzle, are essentially the same hot gas, the cross-sectional area and shape imposed on the effluent by the nozzle is that of the arc. Also, because of the inherent stability, longer and thus higher voltage arcs can often be used than were possible or practicable in the past. The net result from the higher are voltage or power and the reduced cross section of the arc is exceptionally high energy flow per unit cross-sectiorii area at any given current.

Additionally, since the velocity of gas issuing from a nozzle at a given pressure (including the critical or sonic velocity) increases with the temperature, and because arc gas temperatures are the highest generally obtainable, the gas velocity through the nozzle of the invention for a given pressure can be made exceptionally high. Exceptionally high gas velocities are useful in many applications due to the attendant momentum and directed kinetic energy imparted to the efiluent.

The desired momentum and directed kinetic energy of the effluent are achieved by the invention with great economy of gas. At constant pressure the volume of a given weight of gas ideally is proportional to the temperature of the gas. The velocity of gas for a given mass rate of flow through an orifice thus will b higher for a higher temperature gas. Since most, if not all, of the gas in the torch of the invention passes through, and in fact, comprises the are, it is evident that, due to very high gas temperatures, high velocities can be achieved by a minimum expenditure of gas.

It should be emphasized that the arc stream of the invention and the jet of hot gas issuing from the nozzle are one and the same effluent. The jet of gas is the current-carrying arc stream and it thus continues to re ceive electrical energy until it reaches the workpiece. The combination in which a high velocity jet and a high-energy density, current-carrying arc stream are virtually coextensive, produces unique results best exemplified in the use of the invention for the cutting of some metals at speeds, quality of cuts, and economy superior to those of prior arc-cutting processes.

Some of the above and other features are further disclosed below. In any are device, the arc is drawn from one electrode toward another electrode, such as the workpiece, by the potential gradient existing between such electrodes. In unrestricted arcs, this is relatively weak and is sometimes undesirably dominated by extraneous external influences, such as magnetic fields and drafts. The result is an unstable are which, due to known vagaries of motion of the cathode and anode spots, is sometimes erratically and undesirably deflected out of control away from the work point where it is needed. To minimize such undesirable condition, it was sometimes necessary in prior metal welding practice, for example, to hold th electrode tip close to the work, thus increasing its vulnerability to inadvertent, unwanted contamination by the molten work metal. My invention advantageously minimizes such erratic deflections of the are by wall-stabilizing a portion of the length thereof and imparting controlled momentum to the effluent.

Still another feature of the invention is the unique collimation in the cflluent of the energy flow. Due to the divergent or flaring shape of the usual unconfined are as, for example, one used in inert gas shielded-(arc welding, accurate arc length control is desirable in order to achieve a uniform power density on the work with uniform penetration and bead width. In contrast, by control of nozzle geometry, the eflluent of the invention as it issues from the nozzl can be made to maintain its directed motion in the form of a collimated flow of energy having a power intensity that is relatively independent of the arc length.

According to the invention, there is provided a basic" torch that comprises a primary electrode which is mounted adjacent the inlet of a water-cooled nozzle to provide a locus for one end of an arc. The other end of such are is carried by another primary electrode such as the workpiece. A gas stream is delivered to such nozzle so as to issue therefrom with the are toward the work. While it is not necessary that such gas stream be delivered to the inlet of the nozzle under pressure, in some cases the latter is highly beneficial and greatly improves the operation. The gas may be any suitable gas or mixtu re of gases. The basic torch of the invention may fitailored to perform a desired job in controlling the effluent through the use of one or more nozzle orifices of the same or different cross-sectional areas, directions and shapes.

The invention has proved to be exceptionally suitable for cutting (severing) metals when the work itself is a primary electrode, the primary torch electrode is thoriated tungsten, the gas is argon, and the current is direct current-straight polarity (work positive).

The invention includes the use of alternating current with or without superimposed high-frequency, as well as direct current-straight or reverse polarity, for energizing the arc. A convenient adjunct of the invention is the use of a pilot are drawn between the torch electrode and the nozzle which keeps the end of the electrode hot and facilitates the initiation and operation of the main arc. Operations involving the heating and melting of any metal are within the scope of the invention which, however, is not restricted thereto except as claimed.

In the drawings:

Fig. 1 is a perspective view of an elementary form of the invention in which the primary electrodes are a workpiece and a rod;

Fig. 2 is a sectional view of a modification of the invention;

Fig. 3 is a view in side elevation of a prior conventional unrestricted inert gas-shielded arc;

Fig. 4 is a graph illustrating three curves taken at different distances from the electrode of Fig. 3 in which arc-diameter is plotted against arc current;

Fig. 5 is a view partly in the form of a circuit diagnam illustrating a butt-welding operation of the arc torch, parts of which are shown in vertical-longitudinal cross section;

Fig. 6 is a similar view illustrating a cutting (severing) operation of another form of the arc torch;

Fig. 7 is a similar view illustrating a direct currentreverse polarity hook-up of a water-cooled electrode modi fication of the arc torch;

Fig. 8 is a similar view illustrating a fan-shaped are modification of the invention;

Fig. 9 is a view in cross section taken on line 9-9 of Fig. 8;

Fig. 10 is a fragmentary longitudinal-vertical section of a split-arc modification;

Fig. 11 is a cross section taken on line 11-11 of Fig. 10; and

Figs. 12-15 are graphical representations illustrating operating conditions.

It will be understood that the elementary torch modifications of the invention shown in Figs. 1 and 2 are supplied with a suitable gas, such as argon, helium, hydrogen, nitrogen, or mixtures thereof, which gas preferably is caused to How axially in an annular stream about a suitable primary electrode 10 and then through a nozzle 12 provided with an internal passage 13 which characterizes the invention, either by the aspirating action of the arc itself, or by supplying such gas under pressure. Typically, according to the invention, the electrode 10 is of the pencil, rod or stick type provided with an arc-locus tip axially aligned with and adjacent to one end of the nozzle 12. The other primary electrode may, for example, be a metal workpiece (plate) 14. The nozzle 12 may itself also serve as a secondary electrode as pointed out below. In each case the primary electrodes are connected to a suitable D. C. or A. C. source of electric energy by conductors 20 and 22. An extremely hot, electrically conductive efiluent 24 issues from the outlet of the nozzle 12 of the torch.

In each case the nozzle passage 13 laterally shapes, and directs and, in varying degrees, constricts and wallstabilizes the arc-column. Such shaping, wall-stabilizing and constricting of the arc-column by the nozzle passage 13 perform several valuable functions. The voltage of the arc-column can be substantially increased, thus developing more power in the arc stream at a given current. I have found, for example, that, whereas the arc voltage in a prior unconstricted are may be 8-20 volts per inch in argon at 200 amperes of arc current, with the higher values being associated with the column portion very close to the electrodes, the arc voltage in a constricted argon-arc of the invention is no less than about 30 volts per inch in a 4-inch I. D. (inside diameter) nozzle, volts/inch in a 4-inch I. D. nozzle, and to 200 volts/inch in a -inch I. D. nozzle.

The higher voltage and power, and the higher attainable collimation of energy flow, provided by the invention, are demonstrated by the following data, Table I, comparing bead welds made according to the prior art and according to the invention (using cylindrical nozzle geometry as shown in Fig. 5 which is described in detail below) AISI type 304 stainless steel at 175 amperes, DC-SP, 10 I.P.M. welding speed with argon supplied to the torch.

The nozzle 12 may be made of any suitable solid material and may be cooled, if necessary, in any convenient way, for example, copper with water cooling, tungsten with radiative cooling, ceramic with or without water cooling, or the like.

The dimensions of the nozzle vary considerably for various conditions of operation and for various uses. The axial length of any electrically continuous section of the nozzle is limited by a tendency to double arcing which is the establishing of two arcs in series (electrodeto-nozzle, and nozzle-to-work) where only one are (electrode-to-work) is desired. An empirical criterion for continuous stable operation is that the voltage drop along a given length of the arc-column confined within any electrically continuous nozzle portion is preferably less than that voltage which is required to establish an additional anode and cathode. Thus, for example, if it be assumed for a given case that such latter voltage when using argon gas and a water-cooled copper nozzle, is about volts, then a As-inch I.D. nozzle (80 volts/inch arc-column gradient in argon at 160 amperes) is preferably less than A-inch long (the equivalent of 20 volts length). Longer nozzles can be used but are preferably composed of nonconducting material, or comprise electrically isolated sections when they are composed of electrically conductive material.

As shown in Fig. 3, a prior conventional inert gas shielded are 26 between a stick-cathode 10 and a molten [lat anode 28 has the general shape of a rounded cone which, when shielded by an annular stream of argon,

has the observed dimensions noted in Figs. 3 and 4 for are currents between 100 and 400 amperes. The characteristic curves X, Y and Z illustrate how the observed are diameters at 0.1, 0.3, and 6.6 inch from the cathode 10 increase as the arc current increases in each case. By inspection, Figs. 3 and 4 show, for example, that a Ai-inch diameter nozzle of the invention can wall-stabilize and constrict the arc portion represented at 200 amperes, curve X, Fig. 4, and by collimation of the efiluent can project such diameter to the workpiece. At 0.6 inch from electrode tip, for example, this results in an arc crosssectional area of about one-third that of the arc of Fig. 3.

An arc torch T, Fig. 5, that is suitable for welding metal, comprises a copper nozzle 30 having a central socket 32 in which the lower end portion of the electrode 1!) depends in spaced relation to the inner wall and bottom of such socket, providing a passage thercbetween for the arc gas. Such gas flows through an elongated arc passage or orifice 34 that is axially aligned with such electrode. are that operates continuously between the nozzle and such electrode when a source of current S is connected thereto by leads 20, 22 and 38 through a resistor 40, such as a lamp or bank of lamps.

The nozzle 30 is also provided with an annular groove 36 in the bottom thereof that is concentric with the orifice 34, for directing an outer annular stream or envelope 44 of suitable shielding gas, such for example as argon or CO2, about a zone to be melted on the workpiece 14. A main are 42 is initiated by such pilot are, between the end of said electrode 10 and such workpiece 14, when the latter is connected to a terminal of such source by a lead 48. In such case the nozzle is kept cool by force-circulating water through an annular passage surrounding the socket 32.

The torch of Fig. 5 operates very well when the negative side of a D. C. source S is connected to the electrode 1t), and the positive side is connected to leads 38 and 48 by conductor 22. Such torch will also operate Well when connected to an A. C. source of power. In such case lead 48 is connected directly to one ter minal of an A. C. welding source and electrode 10 is connected to the other terminal. A continuously operated 30 amp. D. C. pilot are, for example, will effec- Such passage 34 is elongated and carries a pilot tively initiate, stabilize and maintain a main A. C. welding arc. Such pilot arc may be operated continuously, even during the operation of the main are.

In operation the torch T is moved in the direction of a path to be butt-welded in the workpiece 14, and the efiluent 24, which is shielded from the air by the outer annular shielding gas stream 44, melts a seam 51 in the workpiece, which, as the effluent 24 moves away, cools and solidifies. A remarkable feature of the torch T is that the eflluent 24 is well collimated and produces a remarkably small variance in weld bead dimensions over a wide range of torch elevations with respect to the work as seen in Table I. The torch T is also well suited for flange-welding sheet metal parts at a rapid rate.

A small arc torch like that of Fig. 5 was used to weld .3.007 inch thick stainless sheet at 25 I. P. M. using 15 amperes DS-SP, /4 C. F. H. argon through a A -inch diameter center orifice, and about 25 C. F. H. argon in the surrounding envelope. The efiluent 24 was stable, easily controlled, and had no tendency to wander even at current values of as low as 8 amperes.

As shown in Fig. 6 there is provided a torch T1 of the invention comprising a primary electrode 10 that is axially mounted within a cylindrical barrel 52 in the end of which is secured a nozzle 54 having a central passage 55 into which the lower end of the electrode 10 projects. The discharge section of the passage 55 tapers to an outlet orifice of reduced diameter. The annular wall of the nozzle 54 is spaced from the inner wall of the barrel 52 to provide an annular passage 56, sealed by 0 rings 57, 57, for cooling water which is fed thereto through an inlet 58 and discharged therefrom through an outlet 60.

The nozzle 54 preferably is composed of copper and the electrode 10 of thoriated tungsten. The electrode 10 is connected to the negative side of a direct current source S by lead 20, while the positive side of such source is connected to the work 14 by leads 22 and 48. The nozzle is also connected to the positive side of such source by branch circuit 38 that includes resistance 40 which limits the amount of current to that which is sulficient to maintain a pilot are between the primary electrode 19 and the nozzle 54 which, in this case, constitutes a secondary electrode (anode). A suitable gas is delivered to the interior of barrel 52. In a manner similar to that described for the torch of Fig. 5, the torch of Fig. 6 will also operate well when connected to an A. C. welding power source.

The etfiuent 24 discharged by the torch T1 is well collimated, and with a length up to 1.5 inches, for example, is exceedingly stable. Typical performance data of the torch T1 are as follows: With a 200 ampere arc, 0.5 inch long, a /gg-ll'lCh I. D. nozzle, and 20 C. F. H. of argon, the arc potential is 38 volts, the calculated cflluent velocity is about 1000 F./S., and the heat applied, i. e. delivered, to the workpiece is 5.2 kw. This compares with a conventionally unconstricted argon gas are potential at the same arc length of 19 volts, and heat applied to the workpiece of 2.7 kw. An approximate calculation of the relative power intensities at the work for such examples shows about a ten-fold advantage for the torch of the invention. Any suitable gas which has no harmful elfect on the electrodes may be used.

At higher gas flow rates (30 C. F. H. or more for a /B-ll'lCh l. D. nozzle, for example), the effluent 24 procluces a powerful metal cutting (severing) action. With a /s-inch I. D. nozzle, C. F. H. argon, and 200 amperes of arc energizing current, for example, the effluent can sever, by kerf-melting, a %-inch thick plate of aluminum at a severing (traverse) speed of about I. P. M. Other examples, shown in Table II below, are illustrative of some plate severing speeds obtained according to the invention for various metals using DC-SP and a %-inch 1. D. nozzle.

Table II Thlck- Speed Current Voltage Argon Material (Plat/e) ness (I.P.M.) (Amperes) (Volts) ((1 Eli.)

(inches) 34 144 340 56 l 10 V2 70 880 66 110 A 30 260 G4 100 l 15 260 75 110 M 100 280 69 110 )6 30 270 69 110 M 45 340 66 Ill] V 144 250 54 110 Q 110 460 60 I no In Fig. 7 there is illustrated a modification of the invention comprising an arc torch T2 having a liquidcooled anode 76 that is connected to the positive terminal of a D. C. power source S by means including a lead 78. A combined cup-nozzle 80 of such torch is connected so as to constitute a secondary cathode by being connected to the negative terminal of such source by a branch circuit 82 including a resistor 84. The workpiece W is also connected to such negative terminal by a lead 86. The anode 76 is composed of suitable metal such as copper, and is provided with an elongated axial socket 88 within which is mounted a cooling-water inlet pipe 90 that terminates just above the bottom of such socket, and is spaced from the inner wall of the socket to provide an annular outlet passage for the cooling water.

The arc-locus end of the anode 76 is rounded and spaced from a similarly shaped internal surface of the cup-nozzle 80, providing a gas passage 92 that delivers gas, such as argon, to a passage 94 in the bottom of the cup in line with the tip of such anode. The cup-nozzle 80 is provided with an annular recess 96 that is sealed with a sleeve 98 and O-rings 100, providing an annular cooling-liquid passage into which water is introduced at 102 and discharged at 104.

The effluent 24 produced by the torch T2 when direct current at 240 amperes is supplied to the lead 86 at 50 volts potential between the anode 76 and the work W was used to cut (sever) one-inch thick aluminum plate W at inches/minute, leaving a %-inch wide kerf. In such case 30 C. F. H. of argon was supplied to the torch. A ampere direct current supplied to cup 80 and anode 76 continuously energized a pilot are between the primary anode and the secondary cup-cathode that performs very well in establishing the main are between the primary electrodes 76 and W. The cup 80 and anode 76 are preferably composed of copper, but tungsten or any other suitable metal may be used.

An important novel feature of the invention is that an arc can be controlled according to the invention to produce an etfiuent shaped or split as desired, as shown in Figs. 8 and 10 for example. Figs. 8 and 9 illustrate the phenomenon in which a fan-shaped efiluent V results in conformity with the cross-sectional shape of a passage 115 in a water-cooled nozzle 116 when the gas velocity is sufi'iciently high, 10 C. F. H. of argon, for example, flowing through a 0.10 inch x %-inch slotted nozzle exit. In such case the effluent is stable, the argon being supplied to the annular space 118 between the electrode 10 and the wall of an axial passage 120 in the nozzle.

In the case of Fig. 10, an arc can even be split in two parts by means of a nozzle 125 having two divergent arc passages 126, 128 which originate from a common passage 130 containing the electrode 10. This is most unique and produces stable etfiuents 122, 124 which are suitable for many uses, such as welding and cutting, since they can be given desired shape and direction. Any desired number of efiluents can be provided.

In the present invention the total heat delivered by the efiluent to a workpiece comes from the arc plasma within the nozzle, from the arc-column between workpiece and nozzle, and from varied electrode processes. Analysis of thermal transfer data for argon gas operation shows that at zero gas flow, essentially none of the heat developed by the arc in the nozzle leaves the nozzle, but such heat is lost largely to the cooling water of the nozzle. Most of the heat reaching the work in such case is ac counted for by electrode processes such as electron condensation. (Heating by condensation equals electron current times material work function plus anode fall.)

For example, using DC-SP and a 4-inch I. D. nozzle of %-in-ch length, the heat lost to the nozzle decreases continuously to a minimum of about 40 percent of that developed in the nozzle with increases in argon gas flow up to 20 C. F. H. This means that at 20 C. F. H. roughly 60 percent of the heat developed in the arc plasma within the nozzle is contained in and is discharged with the hot argon issuing from the nozzle. This heat in turn is delivered by the eiflucnt to the workpiece with efficiencies of better than 70 percent for nozzle-to-work distances of /is-iIlCh to Mi-inch.

Approximate quantitative picture of these phenomena is presented in Table III below which uses volts as a convenient measure of energy at the 200 ampere current level (DCSP). A Aa-inch inside diameter by /s-inch length cylindrical nozzle and a fiz-inch external arc length was used.

Table III Zcro Argon Flow 20 C. Fl. II. Argon *low From mk'ww' Volts De Volts De- Volts Volts Dcveloped livcrcd v loped llvcred to Work to Work Arc Plasma in Nozzle... l2 (1 l6 8 Arc Plasma Outside Nozzle. 5 2 0 1 5 Electron Condensation 7 7 7 l 7 Total 24! a an an Efficiency, percent. 35 70 It is thus seen that at 20 C. F. H. argon flow, the power contribution from the arc plasma inside the nozzle is of major importance.

Referring to the graphs shown in Figs. 12-15, curve B. Fig. 12, shows the voltage gradient in the nozzle versus nozzle diameter for cylindrical nozzle geometry. The vertical reference band C in the left of the graph denotes the voltage gradients in an open argon are 26, Fig. 3. As shown, as the nozzle diameter becomes larger (and the arc-column constriction less) the voltage gradient curve B of the arc torch approaches and joins the prior inert gas shielded-refractory electrode are characteristic C. For the smaller nozzle diameters the voltage gradient is many times that of such prior arc gradient C. In Fig. 12 the Aa-inch diameter orifice will constrict the are only very moderately as evidenced by a slight increase in voltage gradient over the minimum represented in band C; the arc portion within the nozzle is, however, very effectively wall-stabilized. Incipient constriction as evidenced by voltage curves analogous to Fig. 12 can be used as a general criterion for the existence of effective wall-stabilization.

Fig. 13 shows power distributions versus gas flows through the nozzle in the arc torch at a fixed current DC-SP (the nozzle is cylindrical and is /s-inch in length). The total electrical power input (volts X amperes) curve E increases almost linearly with gas flow at a rate of about 40-50 watts per C. F. H. gas flow increase. This same nozzle, operated at a lower current, produces a relatively flatter voltage vs. gas flow characteristic. The power deliveredto-work curve F increases rapidly up to 20-30 C. F. H. The power lost-to-nozzle curve G decreases up to 20 C. F. H. and remains at a nearly constant minimum value at higher gas flows. For comparison, the total power (input) line H and the power-to-work line I of a prior unrestricted argon-shielded arc of the same length (%-inch) and current (200 amperes) are shown. The are torch of the invention at 40 C. F. H. through the nozzle, thus delivers 75 percent more power to the work than does the prior conventional argon shielded arc. (The power distribution in prior conventional inert gas shielded arc is not given as a function of gas flow, since any forced movement of the atmosphere in such case has only minor secondary etiects.)

Curves J and K, Fig. 14, illustrate voltage versus current arc-characteristic of the arc torch (with a A's-inch diameter nozzle), and of the open or unconstricted argon shielded arc of the prior art, respectively. It can be seen that the increase in voltage with current, curve J, is much greater in the arc torch. A practical consequence of this is that, in contrast to the prior conventional nonconsumable electrode torch, the main power supply for the arc torch of the invention need not have a drooping voltampere characteristic in order to maintain a controllable degree of variation in the arc current. For example, with a -inch inside diameter by ai -inch length nozzle arc passage, using C. F. H. argon gas, and volts constant voltage DC--SP, the arc length external to the nozzle was changed from A-inch to %-inch with an attendant current change from 100 to 130 amperes. The current in the prior conventional non-consumable argon shielded are would change by several times this amount with the same kind of power source.

Arc torches of the invention have been operated with He, N2, and H2 gases, and with mixtures of such gases with argon. Variations of arc voltage with percent of He, N2, and H2 by volume in argon are shown by the characteristic curves L, M and N, Fig. 15, for DC-SP. However, the invention is not necessarily limited to such gases, since any gas or mixture of gases that is suitable may be used.

Features of the invention include:

1. The nozzle is not a primary electrode, but is only a secondary electrode in those cases involving a pilot are.

2. Since the higher are power developed by constricting the arc is only in part lost to the arc-shaping nozzle, unexpectedly large quantities of additional power go to the workpiece in the form of heat.

3. Since the efiiuent-controlling nozzle is substantially non-consumable, contamination is minimized and commercially useful nozzle life is attained.

4. It is noteworthy that a nozzle composed of an electrical conductor, such as metal, can be operated at all without double arcing" in series with the nozzle, i. e., forming one are between the primary torch electrode and the nozzle and a second are between the nozzle and the work in series circuit relation.

5. It is also noteworthy that the main arc is not extinguished at the gas velocities in the arc-column up to many thousands of feet per second.

6. The prior conventional arc has heretofore been conventionally the most intense (commercial) source for heating metal. The invention excels such prior conventional counterpart as a source of intense heat by many times because:

(a) It can be shaped to reduce the cross-sectional area of the are. For example, an arc of -inch cross section reduced to As-inch is 12 times more intense due to constriction alone.

(b) It increases the heat developed by the are at a given current and length by voltage, and thereby power, increases due to constriction and to the flow of gas much of which is heated to are temperature. For example, at 200 amperes and /2-inch arc length at 80 C. F. H. argon through a fis-inch inside diameter nozzle the power developed in the torch of the invention is more than doubled over that of its prior conventional counterpart.

(c) The calculated net result of the two effects for the 10 last chosen example is an approximately 20-fold increase in efiective power intensity.

7. The cross-sectional shape of the arc efiiuent discharged from the nozzle conforms to the cross-sectional shape of the arc constricting passage even when cylindrical nozzle geometry is not employed, provided the gas velocity is sufficiently high.

8. Another valuable feature is that the are can be made to divide itself spontaneously into multiple efiluents corresponding to available nozzle passages provided therefor.

9. Compared with the characteristic of the prior inert gas shielded-refractory electrode unrestricted-arc, the arc of the invention has a more sharply rising volt-ampere characteristic. Thus, in addition to conventional drooping" characteristic sources of power, the arc torch of the invention can be used with power sources having a more or less flat volt-ampere characteristic.

The term high-pressure are as used herein is discussed (pages 290 and 326) by Cobine in his book, Gaseous Conductors, published in 1941 by McGraw- Hill and is to be understood to relate to self-sustaining gas discharges in the general pressure range above do atmosphere and generally in the current range of a few to thousands of amperes.

I claim:

1. Process which comprises establishing a high-pressure are between an electrode and a workpiece, wall-stabilizing a portion of the length of such arc, to produce and control the shape and direction of an efiluent between the point of such wall-stabilization and said workpiece, and applying the so-controlled effluent to said workpiece.

2. Process which comprises establishing a high-pressure are between an electrode and a workpiece, laterally constricting a portion of the length of such arc to produce, concentrate the heating intensity and control the shape and direction of an efiiuent between the point of such constrction and said workpiece, and applying such efiiuent which is so-controlled to said workpiece.

3. Process as defined by claim 2, in which the workplece is metal and the efliuent is used to melt a bead therein.

4. Process as defined by claim 3, in which an annular stream of suitable gas is used to shield such efiluent and the adjacent metal of the workpiece.

5. Process which comprises discharging a stream of gas through and from a nozzle, establishing through such nozzle 21 high-pressure are between electrodes located adjacent the gas inlet and outlet of such nozzle, one of said electrodes consisting of a workpiece in circuit with such are and toward which gas is directed, and wallstabilizing such are within such nozzle.

6. Process as defined by claim 5, in which a pilot arc is struck between such nozzle and such electrode adjacent the gas inlet for initiating such are to the workpiece.

7. Process of forming, concentrating and directing an effluent which comprises striking an are between spaced primary electrodes one of which comprises a workpiece, and directing such are through a solid provided with an arc constricting passageway that wall-stabilizes and dis charges an arc-gas efiiuent, confines such effluent to a predetermined path, and concentrates the power intensity thereof.

8. Process of melting a selected zone of a metal workpiece which comprises connecting the work-piece and an electrode in circuit with a source of arc current, striking an arc between such electrode and such workpiece, wallstabilizing a portion of the length of such are with a water-cooled nozzle through which such are passes, feeding selected gas to the inlet of such nozzle, discharging the resulting directionally stable efiluent from the outlet of such nozzle, applying such efiiuent to such workpiece, and melting such selected zone of metal therewith.

9. Process as defined by claim 8, in which the metal workpiece is welded by removing the efliuent from the melted metal of such zone, permitting such melted metal to cool and solidify.

10. Process as defined by claim 8, in which the metal workpiece is cut by removing the so-melted metal from the rest of the workpiece.

11. Process which comprises forming a high-pressure are between a non-consumable electrode and a workpiece, passing such are through a cooled-solid nozzle which wall-stabilizes a portion of such arc, and feeding a selected gas through such nozzle for issue therefrom with such are toward such workpiece.

12. The combination comprising means for forming a current-carrying high-pressure arc, means for wall-stabilizing and discharging an effluent comprising such arc and a suitable gas, said means for forming such arc-gas efiluent comprising two electrodes, one of which is a workpiece, and an essentially nonconsumable nozzle through which the arc and gas flow and in which the discharged efiluent is shaped.

13. The combination as defined by claim 12, in which means are provided for supplying the arc power in the form of direct current at reverse polarity.

14. The combination as defined by claim 12, in which means are provided for supplying the arc power in the form of are direct current at straight polarity.

15. The combination as defined by claim 12, in which means are provided for supplying the arc power in the form of alternating current.

16. The combination as defined by claim 12, in which means are provided for establishing a pilot are.

17. An arc torch comprising, in combination, an electrode, a relatively cold annulus provided with an are shaping passage axially aligned with said electrode, means for establishing a high-pressure are through said passage between the end of said electrode and another electrode, means for feeding gas to such passage, the eifect of the relatively cold inner surface of said are shaping passage being to produce a directionally stable etfiuent which issues from such passage.

18. An arc torch comprising the combination of an electrode, an arc modifying nozzle surrounding the tip of said electrode, means for feeding gas to the inlet of said nozzle, and means for connecting said electrode to a source of power for drawing a high-pressure are from the tip of said electrode and through said nozzle to a workpiece which is also connected to such power source, the internal size of said nozzle being such that an effluent issues therefrom that is composed of a jet of gas and are plasma stream, the shape of which efiiuent is determined by the geometry of said nozzle.

19. An arc torch as defined by claim 18, in which the cross-sectional size of the interior of said nozzle is substantially less than that which such are would be naturally in the absence of such nozzle.

20. The combination of a primary electrode in the form of a pencil, a nozzle having an arc-constructing orifice axially aligned with said pencil, the surface of said orifice being spaced from one end of said electrode and an arc-gas effluent producing passage below the end of such electrode, means for cooling said nozzle, said nozzle comprising a secondary electrode, circuit means for connecting said primary and secondary electrodes to terminals of a source of current for energizing an arc therebetween, circuit means for connecting said primary electrode and a workpiece, respectively, to said terminals for energizing another are between the end of said electrode and the workpiece, and means for delivering a suitable gas stream to said annular gas passage.

21. The combination of at least three spaced electrodes at least one of which is provided with an internal cooling-liquid passage, and at least one of which is provided with a passage for producing an arc-gas efiiuent, means for connecting two of said electrodes across a source of power for energizing a main arc, and means including an impedance for connecting such power source across one of said two electrodes and to another electrode for energizing a pilot are.

22. The combination as defined by claim 21, plus means for feeding gas to said passage.

23. An arc torch comprising non-consumable means provided with a plurality of passages for an arc which split such are into a plurality of arc efiluents corresponding to such passages.

24. In combination, a gas shielded arc torch comprising a central electrode having a pointed tip, a watercooled nozzle having a tapered gas passage leading to an arc constricting orifice in axial alignment with said central electrode, circuit means for energizing a direct current pilot arc in the interspace therebetween, means for feeding selected are gas to the annular space between said electrode and nozzle, which gas is discharged from such orifice with such direct current pilot are as a concentratcd stream including ionized gas, and means for connecting said central electrode to a suitable source of current for energizing a high-pressure arc between said electrode and a workpiece, which high-pressure arc is piloted through such are constricting orifice between the tip of said central electrode and said workpiece by such concentrated stream of ionized gas, providing an intense jet-like efiiuent that is heated by both of such arcs.

25. In combination, a gas shielded arc torch comprising a central electrode having a pointed tip, a watercooled copper nozzle having a tapered gas passage leading to an arc constricting orifice in axial alignment with said central electrode, said nozzle being electrically insulated from said central electrode, circuit means for connecting said nozzle and said electrode to a suitable source of current for energizing a direct current pilot arc in the interspace therebetween, means for feeding selected are gas to the annular space between said electrode and nozzle, which gas is discharged from such orifice with such direct current pilot arc as a concentrated stream comprising ionized gas, and means for connecting said central electrode to a suitable source of current for energizing a high-pressure direct current are between said electrode and a workpiece composed of metal, which high-pressure arc is piloted through such are constricting orifice between the tip of said central electrode and said workpiece by such concentrated stream of ionized gas, providing an intense jet-like efi'luent that is heated by both of such arcs.

26. The combination with an electric arc torch comprising a central electrode and a gas cup of metal having an annular gas outlet orifice that is concentric with one end of said central electrode; of a direct current source connected across said electrode and cup for energizing a D. C. pilot-arc between such electrode end and the inside of said orifice, a source of arc gas connected to the annular space between said electrode and orifice for discharging a stream of D. C. pilot-arc ionized gas from such orifice of said cup, and a circuit for energizing a main arc between such electrode end and an external electrode when such D. C. pilot-arc ionized gas stream is applied to such external electrode.

27. The combination with an inert gas shielded arc torch comprising a metal cup from which gas is discharged around a non-consumable metal electrode, which cup and electrode are electrically insulated from each other, of a source of current connected across said cup and electrode, which energizes a D. C. pilot-arc therebetween which keeps the end of said electrode sufficiently hot to initiate a main are between such electrode and a workpiece when the latter are connected to a source of current, and means for connecting a source of current across said electrode and a workpiece for energizing a main arc therebetween. which is initiated by said D. C. pilot-arc.

28. An are torch comprising, in combination, an electrode, a relatively cold annulus provided with an are shaping passage, means for establishing a high-pressure are through said passage between the end of said electrode and another electrode, means for feeding gas to such passage, the effect of the relatively cold inner surface of said are shaping passage being to produce a directionally stable effluent which issues from such passage.

29. An arc torch comprising, in combination, an electrode, a relatively cold nozzle having divergent arc shaping passages which originate from a common passage containing said electrode, means for establishing a split high-pressure are through said passages between the end of said electrode and another electrode, the effect of the relatively cold inner surfaces of said are shaping passages being to produce separate directionally stable effluents which issue from such divergent passages.

References Cited in the file of this patent UNITED STATES PATENTS Taylor Sept. 2, 1941 Coleman May 22, 1900 Mathers Sept. 5, 1911 Embleton Jan. 25, 1938 Wyer May 26, 1942 Herman Jan. 19, 1943 Pakala July 18, 1950 Olzak Sept. 12, 1950 Jordan Feb. 26, 1952 Buch Aug. 17, 1954 Rava Oct. 23, 1956 Briggs Oct. 23, 1956 

